Disable Product Category field in Confirmation only for Limit SC's

Hi Experts,

I want to Disable Product category field in confirmation creation only for limit SC's ,

just want to prevent users to change product category on Limit confirmation creation ,

Please suggest me what is best way to achieve it,

I have tried for webdynpro methods for corresponding view , but there is no post and pre exit

exits for modify method.

Thank you,

Venkat